This invention relates in general to insulation products made from mineral fibers such as fibrous glass and, in particular, to methods and apparatus for controlling product properties by monitoring and controlling moisture in a forming hood.
Fibrous glass insulation products generally comprise randomly-oriented glass fibers bonded together by a cured thermosetting polymeric material. Molten streams of glass are drawn into fibers of random lengths and blown into a forming chamber or hood where they are randomly deposited as a pack onto a moving conveyor or chain. The fibers, while in transit in the forming chamber and while still hot from the drawing operation, are sprayed with an aqueous dispersion or solution of binder. The residual heat from the glass fibers and from the flow of hot gases during the forming operation are sufficient to vaporize much of the water from the binder, thereby concentrating the binder dispersion and depositing binder on the fibers as a viscous liquid with high solids content. Further water may be removed by drying the binder on the fibers. As the water vaporizes, the energy transfer also cools the glass fibers. The uncured fibrous pack is transferred to a curing oven where heated air, for example, is blown through the pack to cure the binder and rigidly bond the glass fibers together in a generally random, three-dimensional structure known as a “blanket.” Sufficient binder is applied and cured so that the fibrous blanket can be compressed for packaging, storage and shipping, yet regains its thickness—a process known as “loft recovery”—when installed.
Vaporization or “flashing” of the binder dispersion in the forming hood is a significant problem for multiple reasons. Environmental concern with binder emissions is a first problem, leading some state and federal regulatory agencies to prohibit the release of binder solids or vaporized gasses into the atmosphere. Secondly, binder can accumulate on the equipment in the forming hood, including the chain, the side hoodwalls and downstream air ventilation equipment, causing higher costs for increased binder usage and for cleaning the binder from the equipment. Finally, physical properties of the insulation pack may be adversely impacted by binder concentration and viscosity. Binder and/or glass fibers that stick to hood walls can dislodge into the pack causing wet spots or splotches of higher density. If the binder is too viscous or tacky, the pack may exhibit signs of non-uniform density (i.e. vertical weight distribution); and may become “boardy” at a bottom layer and/or otherwise exhibit increased density near the bottom. In addition, a product may not achieve a desired thickness prior to curing in the oven, and may not meet intended specifications for R-value.
Some of these problems have been partially addressed in the prior art. Due to the growing pack thickness, binder particulates tend to become entrapped to a greater degree at later fiberizing units than at initial ones. The solids that pass through the pack and into exhaust streams tend to come primarily from the first fiberizing units. As one solution to alleviate this problem, sacrificial cooling water or liquid may be sprayed on the hot fiber veil at these fiberizing units to cool the hot fibers before the application of binder. This tends to minimize vaporization of the binder; however, the addition of coolant water causes other problems such as waste water control and wetter packs that require further energy to cure in the drying oven. Thus, to facilitate emissions and water control, manufacturers tend to use cooling water preferentially at initial fiberizing units where no pack is yet developed, and reduce the water usage at subsequent fiberizing units where the pack is building and can filter particulates from the emissions streams.
U.S. Pat. No. 3,877,911 (1975) to Borst describes a multi-ring manifold disposed about the exit end of pivotable lapper bucket 74. A first ring 106 supplies coolant water and a second ring 108 supplies air pressure for atomization of the water. Borst discloses (col. 6) that with water pressure at 90-120 psi and air pressure at 5-15 psi, little atomization occurs and the streams have sufficient kinetic energy to penetrate the veil and impinge on one another in the interior of the veil (FIG. 4). At the same water pressure but at 16-50 psi air pressure, some atomization occurs but the stream is still able to penetrate and cool the veil (FIG. 5).
US Patent Publication 2008-0156041 and WO 2008/085,461, to Cooper, describe coolant spray rings and binder spray rings having different types of nozzles spaced around the rings. The different nozzles have different spray angle properties and include atomizing caps.
U.S. Pat. No. 7,435,444 to Freeman, et al., discloses a process for using a moisture sensor to measure the moisture level of an uncured pack as it leaves the forming area. If the moisture level is too high compared to a pre-set value, a control unit changes one or more of the process conditions to reduce the residual moisture.